1. Field of the Invention
The present invention relates to a bus line system suitable for use for example in an AV system.
2. Description of the Related Art
In AV systems, electronic units such as a VTR and an LDP (laser disk player) are arranged to be centrally controlled by an AV center. With such arrangement, a plurality of units can be externally combined for use. For example, an LDP 4 and a VTR 3 can be brought into a cascade connection through a D2B bus line 21, as shown in FIG. 3, so that a video disk is reproduced by the LDP 4 and the reproduced signal is supplied to the VTR 3 and, thereby, a video signal reproduced from a video disk is recorded on a video tape. Such recording operations can be performed under instructions from the AV center 1.
In the AV center 1, a ROM 13, which is formed of a plurality of modules with predetermined programs written therein, is connected with a CPU 12 and a RAM 14 through an internal bus line 22, and between the internal bus line 22 and the D2B bus line 21, there is provided a communication IC 18 so that controlling operations between the AV center 1 and external units are performed therethrough.
Within the ROM 13, there are provided a TV main routine for controlling a TV system, a TV-D2B interface module for controlling an interface between the TV and the D2B bus line, a D2B module for switching inputs and outputs of TV monitor/tuner/AV controller, a D2B protocol module for D2B protocol control, and a D2B communication IC control module for controlling the D2B communication IC, each of which is a module with a predetermined program written therein.
Of such prior art systems, some have a frame buffer 18a within the communication IC 18 and others have no such frame buffer in the communication IC 18. In order to have a system adapted to such different types of communication ICs, the program in the D2B communication IC control module must be changed according to each type of the communication ICs. More specifically, when the communication IC without a frame buffer is used, the data transfer must be processed in units of bits and, hence, the D2B communication IC control module must be changed accordingly.